The impact of air pollution, e.g., in urban environments is an important issue due to both acute and chronic effects on human health. Present day urban environments are mostly dominated by traffic emissions, e.g., chemically transformed hydrocarbons such as emitted by motor vehicles. For example, main traffic-related pollutants are CO, NOx, SO2; hydrocarbons, and particles. Combustion also produces a mixture of NO2 and NO. Other pollutants (emissions) include particulate matter (e.g., PM less than 2.5 microns (PM2.5) and less than 10 microns (PM10)) and volatile organic compounds (VOCs).
In an example “local” (spatial) area or region, concentration of the pollutants is influenced by transmission, diffusion and emission processes happening in the atmosphere.